IGHMBP2 and motor neuron disorder: Mutations in the Immunoglobulin Mu DNA Binding Protein 2 (IGHMBP2) gene cause Spinal Muscular Atrophy with Respiratory Distress type 1 (SMARD1), a rare, infantile, and fatal motor neuron disease, as well as the milder Charcot-Marie-Tooth disease type 2S (CMT2S).